Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall 11 Chapter 3: Customize, Analyze, and Summarize Query Data Exploring Microsoft Office Access 2007

2 Objectives Understand the order of precedence Create a calculated field in a query Create expressions with the Expression Builder

3 Objectives (continued) Create and edit Access functions Perform date arithmetic Create and work with data aggregates

4 Order of Precedence Rules for establishing the sequence by which values are calculated in an expression Failure to follow results in faulty calculations

5 Order of Precedence Order of precedence from top to bottomUse this symbol Parenthesis() Exponentiation^ Multiplication, division*, / Addition, subtraction +, -

6 Understand Expressions Expressions are formulas based on existing fields  Result in a new field called a calculated field  Used primarily in queries, reports and forms Expressions may include  The names of fields, controls or properties  Operators like +, *, or ()  Functions, constants or values

7 What Are Expressions Used For? You can use an expression to:  perform a calculation  retrieve the value of a field or control  supply criteria to a query  create calculated controls and fields  define a grouping level for a report Result of a calculation in a report formed by using an expression

8 Parts of an Expression Constants: a named item whose value remains constant while Access is running Values: literal values such as the number 1.75 or the word “Hello” [Price] * [Quantity_On_Hand] * 0.7 Identifiers Operator Value

9 Creating a Calculated Field Use correct syntax  Assign a descriptive name to the field  Enclose field names in brackets Total Value: [Price] * [Quantity_On_Hand] Descriptive name for new field preceded with colon (:) Expression using existing fields in a database Use correct syntaxAssign a descriptive name to the fieldEnclose field names in bracketsUse correct syntaxAssign a descriptive name to the fieldEnclose field names in brackets

10 Calculated Field in a Query Calculated Field Query Design View A calculated field is added to a blank column in the design grid

11 Saving a Query with a Calculated Field Does not change the data in the database  Only the query structure is saved  Allows new data to be added to a table that is associated with a query When query executed again, includes the values of the new table data

12 Expression Builder Used to formulate the expressions in a calculated field

13 Expression Builder Use expressions to add, subtract, multiply, and divide the values in two or more fields/ controls Fields available in current query Expand folders by clicking plus sign

14 The Expression Builder Work Area All expressions begin with an equal sign Logic and operand symbols may be either typed or clicked in the area underneath the work area Double-click fields to add them to the work area Logical and operand symbols Work area with expression

15 Access Functions Predesigned formulas that calculate commonly used expressions Payment function in work area Function categories

16 Access Functions Some functions require arguments  A value that provides input to the function  Separate multiple arguments with commas Arguments separated by commas

17 The IIF Function Evaluates a condition Executes one action when the expression Alternate action when the condition is false The IIF function syntax in the work area of the expression builder

18 Example of IIF Function Displays the message “In Stock” if value of 1 or greater Otherwise “Out of Stock” will be displayed =IIF(Quantity_on_Hand] >= 1, “In Stock”, “Out of Stock”) Arguments of IIF function separated by commas

19 Performing Date Arithmetic Access stores dates as serial numbers which allows calculation of dates no matter the format entered Calculated field using dates Query results from date calculation

20 Variations of DatePart Function =DatePart(“q”, “01/22/2007”)  Displays the quarter in which the given date falls =DatePart(“h”, Now())  Displays the hour part of the current date =DatePart(“d”, Now())  Displays the day part of the current date

21 Variations of the DateDiff Function =DateDiff(“d”, [orderdate],[shippeddate])  Displays the number f days between ordering and shipping =DateDiff(“m”,#01/06/2006#, #07/23/2007#)  Displays the number of months between the two dates =DateDiff(“d”,[dateborn], Now())  Displays the number of days between the dateborn field and the current date

22 Data Aggregates Data aggregation allows summarization and consolidation of data

23 Performing an Aggregate Calculation in Datasheet View Must be in a a numeric or currency field Click Totals in the Records group Choose the aggregate function desired Aggregate functions displayed by clicking the arrow next to Total

24 How do Aggregate Functions Handle Null Values? When using the Avg function, null fields ignored When using the Count function, null fields are not included unless an asterisk (*) is used as the argument for the function

25 How do Aggregate Functions Handle Null Values? (continued) Examples  Count(*) will include null fields in the calculation  Count(records) will not include null fields The Sum function ignores null values

26 Add a Total Row in a Query The total row can be added to the design grid by clicking the Totals Icon Totals Icon Total row added to the query

27 Use a Totals Query to Group Organizes query results into groups Only use the field or fields that you want to total and the grouping field Grouping field Field to be totaled